Using my 3D printer to fix broken stuff around the house

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Avoid sharp internal corners, wherever you can make them rounded with at least couple millimeters diameter. (This goes for laser-cutting as well.) Outer edges can be sharp (though then you may be running into them and it is more painful than if they are rounded), inner ones are places for stress concentration, where cracks will start.

The adhesion of the layers is sometimes not perfect. Make the loads go parallel to the layers, if you can, avoid load directions where the layers would be peeled apart.

Be aware of the levers present in the design. Get the loads carried as close to their origin as you can; a long lever will magnify the strength easily way past the strength of the material.

In some cases you can make holes in the part that will serve as crack arrestors; if it starts cracking, try to guide the crack to a round hole where it then will likely get stopped. And/or widen the part, like the crack arresting belts that were on the Liberty ships. Steel, plastic, same principle.

And design conservatively. The more margin for the strength, the longer the lifetime despite unexpected/unplanned higher loads.



I know I’d never make my money back on a 3D printer, but ever since I first saw them my thought has been that I could use them to make replacement battery compartments on TV/DVD/etc remote controls or similar small plastic parts that break frequently.

Whenever I tell people of my idea, they usually say that their solution of duct tape is sufficient.


nice thingamajig.

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What??? But you could make a little hook and fix some broken thing! Think of all the broken things!

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Technically, that’s a dohookey, but congrats on the most excellent repair.


What about something better - make alternative battery covers so you can store there a small Li-ion battery and a microUSB charger, or perhaps a supercap with either a similar USB charger (attach to a phone charger for half a minute, have remotes working for next couple days) or an energy harvesting solar cell?

Voila - no need to buy batteries anymore, never find the batteries dead at the worst moment!

(You can use a white LED in forward direction as a pretty good alternative to a Zener diode when you need 2.5 to 3 volts for remotes. Similarly, red one works at around 1.2V, for those little coin cells common in calipers.)

(Also, you can tape several remotes together to a ball-o’-buttons and share their batteries or the alternative power supply.)


Thanks Shaddack! Very useful. I use Tinkercad, and it is not easy to make radii, unfortunately.

Go for 45-degree (or, slightly better, 30-deg, anything above that is in the territory of diminishing returns) angles then. A crude approximation of a radius, indeed, but still WAY better than a straight 90-deg stress-bait.

Edit: Or go OpenSCAD. I swear on that thing. You can even do tricks like generating the .scad file by another process, e.g. a python or even shell script, then calling openscad from commandline to generate you the .dxf or .stl file, and automate the entire process. Parts can be made not only from primitives (cube, sphere, cylinder) but also by extrusion of an imported dxf curve or polygon defined as a point array (incl. rotation, for e.g. threads). There are also libraries of more complex predefined shapes Out There, and many objects in it can be acquired from e.g. Thingiverse.
For an example (not .stl but .dxf) check out this:
The snap-on locks are an example of how to do rounded corners.
Beware, the code is a bit rough, was not originally intended to be published. Raw data for raw nerves.


Next time, Mark, 3D-print yourself an automatic ice maker for the fridge. Much nicer.

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Hey, can I ask what kind of printer you’re using? Starting to get intrigued by the idea, both for tinkering like you’re doing and making models for my ESL classes. Can’t afford anything pricey (English teachers in Taiwan aren’t exactly loaded) but would rather not get a bargain basement one that breaks in a few months either.

Try openSCAD. Full, programmatic control of your object. Object reuse, compound objects as included files. It has a new precision IDE for rendering your drawings. Most people go with some kind of CAD. I like openSCAD because it skips all that annoying interface crap that you have to learn for each piece of CAD software. Instead, you’ll learn a language. All learning goes directly towards making things, not “getting good with an interface” that will change again when they update the software. Plus there are hundreds of routines and objects online that you can grab & use or modify. OK enough fanboy about openSCAD. It is hard to learn. But so many benefits.


Hey just saw your rave re openSCAD. It is harder to use than a fresh learn of any cad program. But the results are amazing. So precise. And I rely on things others have done all the time. I am faster on it than any cad program, now.



Not only that - you can also make the parts in a parametric way - the dimensions can be calculated from variables (which can be set in the code, or even passed to OpenSCAD via a commandline parameter for automation, e.g. when a set of different-sized parts is needed to be generated from the same drawing).

The parts can be defined as function calls. A whole tray of parts can be made by calling the same “function” (they call them modules), with the appropriate translate() call, from a pair of nested for cycles. The parts can be identical or some parameter can be passed as a variable via the module call.

GUIs and IDEs suck.The cognitive overhead is rarely worth it. At least until they get better and the user interface matures into augmented or immersion VR with haptic feedback.

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Another vote for OpenSCAD, it is a brilliant GUI for a world of pure line by line coded geometry. If you can visualize numbers it is the best for fast results IMHO. The trick is learning how and where to join or blend several shapes to get something like a reasonable shoe sole.
I have a friend who loves SolidWorks, I just couldn’t waste the time learning how to work the program to get to making stuff, plus the newest version doesn’t want to run in a Win7 VirtualBox VM on my single user license(running Ubuntu Linux).
Best use for my 3D printer was making soles and ankle supports for tiny baby shoes. My little girl has Down’s(can cause super slow growth, cute as a button) and her legs and feet grow super slowly. At two now, she wears the smallest size baby shoes as a comfort layer/upper, we(with advice form her PT) attached the sole/ankle support printed with flexible polyurethane and then attached it with Gorilla Glue which is also PU. Works well so far, and at every increase in size I save about $200 which goes a long way to repaying the printer I had until then been making circuit board enclosures and around the house and toy parts like Mark’s on.


Wouldn’t something this irregular be more suitable for a polygon extrusion? Either as manually entered x-y coordinate pair, or drawn in something else and converted to the point array (and included in the drawing) in an external script - draw on paper, curve-trace into a sequence of lines, extract the line edges?

Could be potentially also used for 3d structures, layered from e.g. 1-2mm thick layers. Make a 3d scan, slice it, curve-trace each slice, create polygons, stack the extrusions. Then add other objects (or subtract, e.g. for holes) as desired. If there aren’t way too many layers, should be feasible.

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Yep. I do this ALL the time. For example, bolt holes. There are lots of more complex examples, but bolt holes are the most universal pain in the butt to get right with 3D printing. ABS shrinks, and if your printer is not perfectly calibrated, it shrinks more or less than the known 8%.

How do you calculate this and deal with it?

I don’t.

I make sure that my bolt hole diameters are controlled by a variable at the top of my file. I print just a small chunk of my file with 1 hole (or a small circle with that bolt hole in the middle), check that hole against the bolt, adjust the variable in my file and then print for real.

There are other techniques. You can drill press out your holes to the exact diameter of a drill bit. That’s fine. I do that a lot too. Sometimes parts are too small to work with in a drill press.

Or I use that bolt hole variable in my openSCAD file to adjust roughly for the bolts that I have on hand. Sometimes I have a collection of random sized bolts, don’t feel like going to the store to hunt down more, and I can just change all the holes to what I need, print and be on my way. Super easy with master variables.

In Sketchup, you can make a bolt hole a component for reuse, make sure it is grouped and then alter it once and have that reflected multiple times through the drawing. It’s not like that’s impossible in other programs. I find it easier in OpenSCAD to just change a number at the top of my file and be done with it.

Again, some people are visual, some are programmatic, some are both. I use Blender a lot on STLs. When I scanned my own head with a Skanect, I had a huge dent in the top that I had to fix. It looked like I had been hit by an iron pipe. 3D scanners are terrible for tops of domes. Could I do that dome fix in openScad? Uhhhh, no. Not easily. In Blender, I just lifted all the triangles and bulged out the dent so my head looked more normal shaped. Click clickity click, done.

Different tools for different purposes.

De-novo creation of functional objects, drawn parametrically perfect? Uhh that’s a no-dented-brainer: openSCAD.

Creation of more organic shapes, editing organic shapes, or interested in textures and 3D rendering or animations? Blender.

More comfortable using the keyboard like a console to twiddle special keys while you mouse around tools from a tools pallette? Then any CAD program is your ticket.

Previously trained on CAD, for work or some other interest? Then stick with what you know, no harm in that.


If I were using openSCAD for insoles, I would isolate the surfaces on the sole that need to change. Parametrize those surfaces, so they could be resized independently. Put them together on an unchanging base, like the very middle part of the sole that won’t change shape, or a “frame” or something like that that ties them all together and keeps the shape solid. That way for each new sole, the parts have been predefined and you will just need to measure those new surfaces on your baby’s feet, make the alterations in the file to only the changed components.


Oh hey! Test tube rack! NICE!

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Notice the code for converting the OpenSCADs DXF to something sensible (LINE to LWPOLYLINE), linked from the page. And help yourself if you’re doing any laser cutting.